The good news is that the largest cyberattack in history is over, and the Net is still standing. The bad news: It could happen again.

The Internet was caught in the crossfire between Spamhaus, a Europe-based non-profit that fights spam, and CyberBunker, a Dutch hosting facility. Spamhaus said it traced substantial streams of spam emanating from CyberBunker, and they put CyberBunker on a blacklist they send to e-mail services, thus resulting in millions of inboxes being blocked from those streams.

Spamhaus' efforts have been estimated to filter out an estimated 80 percent of spam, and many industry observers consider it critical to maintaining a workable global e-mail system. CyberBunker says it is "the only true independent hosting provider in the world," and it will allow customers to host anything, anonymously, except "child porn and anything related to terrorism."

'Scourge of the Internet'

CyberBunker countered the blacklisting with the largest Distributed Denial of Service (DDoS) attack in history. The attack centered on Spamhaus's DNS servers, which are deliberately spread around the globe in order to lessen any counterattack, but the downside was that the volume of the attack was so great, the spillover then clogged the Net around the world. According to Spamhaus, the attacks at their peak were about 300 gigabits per second, compared with attacks against major banks that average in the 50 Gbps range.

During the attack, Spamhaus requested help from California-based security firm CloudFlare. The attackers used an amplified DNS reflection technique, in which a DNS request is sent that pretends to come from the victim site, and the unsecured DNS responds to the site. DNS servers that have not been properly secured can amplify an incoming request, resulting in responses that could be 50 times the request. When those responses are amplified, the can overwhelm the victim site.

Domain Name System computers translate the text in Web addresses into numerical IP addresses that computers use, so if a DNS server is unavailable, Web users routed to that server cannot access Web sites.

In a posting on its corporate blog last week, CloudFlare's Matthew Prince joined others who have noted that DNS servers are a vulnerable spot in the Web.

"Open DNS resolvers are quickly becoming the scourge of the Internet," Prince wrote, "and the size of these attacks will only continue to rise until all providers make a concerted effort to close them."

CyberBunker Takes Credit

To counter the attack, CloudFlare used a technology called AnyCast, in which the company's data centers around the world present the same IP address, and the traffic is redirected -- and thinned out -- among the centers. In retaliation, the attackers directed their fire directly at CloudFlare, and then moved upstream to attack CloudFlare's bandwidth providers. The overflow caused major problems for Internet users, particularly in Europe.

The New York Times reported that CyberBunker has taken credit for the attack. The Dutch Web site hosting service has noted that "nobody every deputized Spamhaus to determine what goes and does not go on the Internet." Spamhaus, however, only offers lists to e-mail providers, who then determine which sources to block.

'Fat, Juicy Target'

CyberBunker's Web site boasts that "Dutch authorities and the police," as well as a Dutch SWAT team, have "made several attempts to enter the bunker by force," but none of the attempts were successful. The company is housed in a building referenced by its name --
a five-story former NATO bunker.

Peter Firstbrook, an analyst at Gartner, noted that "DNS is a pretty big, fat, juicy target," and added that, overall, it is not yet "a secure technology." He pointed out that CyberBunker "is not really serving its own interests" in this kind of attack.

To shame hosting providers into securing their DNS, CloudFlare has been publishing the names of providers that maintain the largest number of unsecured DNS resolvers, a tactic which the company said has decreased open DNS resolvers by 30 percent over four months.